This one copped a little abuse, here we give it a thorough going over and dig into some details of your typical Mesa designs before firing it up and gingerly taking some measurements.
Thanks for these great vids. As a guitar player a lot of the information goes over my head however even I find the layout of this Mesa staggering. All the best from London.
The work of "Santa" ? More like the work of Krumpus, because my hands freeze up and suffer serious "Krumpuses" from trying to change parts in such tight spaces and close corners....😁
Speaking of meter probes, I have a set of probes I made with *notched*, not pointed, tips, primarily for checking bias at the individual emitter resistors of high power solid-state hifi amps with multiple MOSFET transistors (like ADCOM, B&K, etc) ---- a situation where the probes dare not slip off the component leads and touch anything adjacent or disaster will result. They're handy for working on amps like this one as well.
Awesome video with great information! You know a lot more about this stuff than I do, but you mentioned more to the story as far as the PCB layout, and I have some insight on that. The amp you have there is a Rev G, and the PCB for that is basically the same exact layout/design from when the dual rectifier was first in prototyping in 1992. Saying it was designed on a computer from the 80s is not an exaggeration - that's exactly the case here. They made these amps the same way from 1992-2000 with no changes to the PCB design. It's easy to look back in hindsight and wonder why they did things that way but it's just old school design with a lot of mistakes, hoping to push the envelope. At the time, stuff like the LDR channel switching/customizing was basically unheard of. Before 1992, there weren't a lot of feature-heavy amps around, not that a 2 channel recto seems that way now, but for the time it was pretty advanced. I recently bought a Rev F (dated 1992 on the inside of the chassis). The C31 grid coupling cap has most of the text melted off and the R233 resistor looks like it was similarly damaged. And just like you mention, whoever tried to repair must've pulled out the eyelet, because they actually had to cut a trace on the board and place a new small wire there, and both the R233 and R232 resistors are new ones (not the same tan colored original ones). The scary thing is despite this clear damage, they had replaced the fuse with a 5A one, instead of the recommended 4A. I've already fixed that - and the amp sounds fantastic - but I'll admit I think I'm going to have a closer look at that cap and possibly replace both C31 and C32 to make sure there's no lingering issues that could damage my output transformer.
That’s not really much of an excuse… I’m working on a Trace Elliot Hexa Valve at the minute. From 1990. It has a clear, well thought out PCB layout, nothing looks crammed in there etc. Mesa’s PCB right here should’ve been used as the prototype for a more refined design.
@@Jonathan_Doe_ Hey, totally agreed. If you think this Mesa is bad, you should see a 1990 Mark IV! They've never been particularly fussed about ease of repair or extreme long term reliability. But - remember you're comparing a much simpler design, single channel, no complex switching etc so of course it's a simpler/easier PCB.
Other Mesa issues - undervalued poly film caps. They use the 400v Orange Drops instead of the 600v, so they inevitably become leaky from too much voltage and allow AC to leak through, which of course blows everything. "Engineering"
Yes, a good point there, mate. True WORDS! I'll try to do a recommended upgrade video on each amp as it comes in next year. A lot of work though, as I hope you'd understand.
@@BradsGuitarGarage Absolutely. The only time I'd go after them is if they were, in fact, leaking and causing grid stopper and plate problems. Otherwise, I wouldn't touch them. That's way too much work. Also, I'd love an upgrade video like that, especially for common workhorse amps, like the Blues Junior or Hot Rod Deluxe, which have their own pain in the butt issues for replacing components.
Speaking of variacs that are not accurately labeled or metered, test all your power conditioners with readouts too. I have a Furman that would always read like five volts or so under the actual mains , for some reason now after some use it is pretty accurate..
Ever worked on one of the newer Mark series mesas? they look like a computer inside. I am in the UK and i have a UK export-model 240v mesa dual rectifier (mid 2000's model) and it has a mains fuse only, no HT fuse. I don't know if its a legal requirement if but if it is, nobody is checking. I have a couple other tube amps that i bought in the UK that have mains fuse only also.
A review of whatever probes you are using would be helpful. One of the things that I have noticed unfortunately is that many modern probes are made with a wire that is far too thin and probably not rated for 600 V and up like we need it to be for working on tube amps. By the way, Extend-A-Probes with an insulated center steel rod that can slide out through the hollow handle are very handy for getting in and taking measurements in tight spots, but the new ones aren't made as well as the older ones, and it might not be possible to put a heavier wire on them.
Yes, I'll make some sort of test jig in the future to count flex cycles and purchase several different test leads at different price points to punish and report the results. This is all the sort of stuff I can afford to do when the subscriber point gets up and I start seeing a little revenue to play with to make video content.
Have you checked out the Brymen multimeters? I've got a 789 and the probes are nice (and silicone) and the meter is similar to my fluke 187. I love it!
Great video Brad. Best Amp repair tuition on RU-vid. Are you a qualified technician or self taught. I only ask because I like want do some amp repairs but not sure on what training I should have .I
Qualified in audio engineering and talking shit, but self taught on the electronics side, unfortunately. Getting certified training is highly recommended. The problem is that it's a rather specialised field now. Most training focuses on either electrical engineering, like power distribution networks etc, or communications. Some of each is applicable, and the fundamentals they'd hammer in to you at the start are essential, but there would be a lot of irrelevant course material. Of course, going into electrical engineering or communications would be a better strategy from a job security and financial point of view, anyway!
An individual is required to hold a license to work on electrical installations, but appliances only require an electrical inspection and testing qualification which I hold from a module in the audio engineering courses over 3 years.
An anagram yes, but they also both come from fire... and I think they are both red. Additionally, both are involved in the consequences of being bad or good. They both harness the energy of goats... Or reindeer... which is kind of like a goat. Maybe. I can tell a goat by the smell... What were we talking about? Oh yeah - People are freaking me out about how Mesa Boogie stuff is difficult or weird... or even diabolical to work on... Some have suggested that the best thing is to take it to Mesa themselves. I have a couple of Bass 400+ amps that need things done to them. I can fix obvious things myself... but as far as taking measurements and setting biases and stuff... Well, I might know some people... I do know not to mess with any aspect of something of which I am unsure whether I know thoroughly or not. 'Anyone have any wise words on how this particular amp is going to try to trick or otherwise make miserable, the individual attempting to repair it, that they'd like to share? Even if Those words are "Don't open that Pandora's box of deceptions, false leads, and shattered dreams unless you feel lucky", I still would value and appreciate the input. Cheers... Brad, and fellow travelers. peace and love.
@@BradsGuitarGarage I know some high frequency guys are scared of the angles, but audio frequencies are hardly high frequency. Hand taped boards were quaint at one point, but now it just feels like the one dude at Mesa who lays out board is some 75yo who no one wants to argue with.
This cracked me up! When in college in Nashville, TN, in the late 90s, the old surplus electrics store had a blowout sale and I bought some tube power transformers. I ran into some old school audiophool that very quickly explained to me that I needed to avoid right angles in my circuit designs. I was like "but...that's not how it works." He disagreed! I have no idea how we even got to that so quickly. Maybe I mentioned Hiwatt and the neat wiring and right angles? Mostly I just wish I'd bought more of those transformers, but I still laugh thinking about that fella. Thanks for the reminder!
@@BradsGuitarGarage they go as far as saying there is a tonal reason why the design such shitty pcbs. Maybe they don't use the word shitty, but you get the point
I had a look and that looks unlike any Mesa PCB I've ever seen. That one is done with an EDA package of some description. Not sure what model that one would be from. Typically they have the hand written white silk screen layer and the rounded corners on all the traces with a hand drawn feel like the one in my video.
Hi my friend! My dual has a problem with fx loop. When fx loop is active SOLO and OUTPUT doesn't work properly, sounds very low. :( in bypass all channel master works and the volume is perfect. I thought was V4 but isn't.
We get it, you hate Mesa but you don't have to pick apart every little detail that you don't like and shit all over your customer's amp every time you get a Mesa Boogie.
Mesa shit on themselves. My job is to wipe their arse. This customer and every other with a Mesa were very appreciative of the intricate detail I go into on their amps and they love watching the videos. No offense intended, but the reality is that their opinion is way more important than a random RU-vid commenter's.
